Cellulose forms the basic structural component of plant cell walls where it exists in the form of cellulose fibres. The use of cellulose extracted from plant material attracts interest because, generally, the cellulose has good strength, stiffness, biodegradability and renewability properties. It is known to reinforce materials such as plastics materials and epoxy resins, with coarse plant fibres from hemp and flax, for example. It is known to use chemically modified cellulose, such as hydroxyethyl cellulose, to increase the viscosity of an aqueous medium such as an emulsion.
However, the production of such chemically modified cellulose is energy intensive, involving a number of treatment steps. Cellulose fibres can be broken down to the substructures of microfibrils and nanofibrils. More recently, the use of these highly purified cellulose substructures as additives for modifying the physical properties of a material has attracted interest. In particular, it is known that some microfibrilar and nanofibrilar cellulose compositions can have a high viscosity in water. Such high viscosity compositions could be useful as viscosity modifiers.
The processing of untreated plant material to obtain microfibrillar and nanofibrillar cellulose compositions is also energy intensive and involves a number of stages including various chemical treatments and homogenisation through, for example, shear mixing or high pressure release or through grinding, filtration and pressing. Generally, the larger the number of process stages required, the more energy is required to produce the end product. There is a need for alternative and/or improved viscosity modifiers. There is a need to provide an alternative cellulose-containing material that can be produced from plants and that can be used as a viscosity modifier. There is a need to provide a simpler, less energy-intensive process of producing high viscosity cellulose-containing material from plants. Also, some of the commonly used chemical treatment steps, such as acid or alkali hydrolysis of plant material, can take a long time. There is a need to provide a more efficient process for extracting a useful cellulose-containing material from plants. More particularly, there is a need to provide a more efficient process of producing a high viscosity cellulose-containing material from plants.
Most known processes of producing cellulose-containing compositions from plants produce a composition having a particular characteristic viscosity or a narrow range of viscosities as measured at a particular concentration in water. Thus, in order to produce a wide range of different viscosity grades of cellulose-containing material, the manufacturer has to change between different reaction systems. This may involve the cleaning of a reactor in order to change reaction systems and product. This has wastage implications, both in terms of downtime and loss of reagents. It would be advantageous to have one reaction system for the breakdown of plant material that could be easily controlled to produce cellulose-containing material having a predetermined viscosity chosen from a wide range of possible viscosities.
Further, it is desirable that the wide range of viscosities are a wide range of viscosities that can be achieved by the material at low concentrations in water, such as 1 wt % or less (unless specified otherwise, all references to weight (wt) herein are references to dry weight). This is not easily achieved as the chemical/biological breakdown of plant material involves complex mechanisms which are not fully understood. It is also desirable to provide a process for preparing cellulose-containing material which process is capable of providing and can be controlled to provide cellulose-containing compositions of different viscosities, i.e. can be controlled to provide both cellulose-containing compositions having a relatively high viscosity at low concentrations in water and cellulose compositions having a relatively low viscosity at low concentrations in water.
For many of the end uses of cellulose-containing material processed from plants, it is necessary to decolourise the material to some extent. Decolourising cellulose-containing material produced from plants often involves additional chemical/biological treatments which increase the overall processing time and may reduce yields. It is therefore desirable to provide an improved and efficient process for preparing such processed plant material which process involves decolourising the material. It is also desirable to provide a process for preparing cellulose-containing material which process involves decolourising the material and which process can be controlled to provide cellulose-containing compositions of different viscosities. There is also a need for a process for preparing high viscosity cellulose-containing material from plants which process also involves decolourising the material.
The present invention seeks to provide a new method of producing cellulose-containing material from plant matter which alleviates one or more of the above problems. Further the invention seeks to provide new compositions comprising cellulose and uses for same.